Case history
A 19-year-old student presented with progressive diplopia with left lateral gaze. Ophthalmologic examination showed a left partial cranial nerve VI palsy. The remainder of her neurological exam was normal.

MRI with contrast showed a 24-x-17-x-19-mm avidly enhancing lesion of the petrous apex, extending inferiorly to the foramen magnum and laterally to the internal auditory canal. CT showed that the lesion was destroying bone and extending directly to the posterior fossa dura and the petrous carotid canal.

The patient underwent an expanded endoscopic endonasal approach augmented by a novel right sublabial transmaxillary endoscopic approach to the clivus and contralateral left petrous apex. A lumbar drain was placed at the time of surgery in the event of a cerebrospinal fluid leak. There was no CSF leak at surgery, and the drain was discontinued at the end of the procedure.

Her postoperative course was unremarkable other than spinal headaches related to lumbar drain placement. These were treated with an epidural blood patch.

Intraoperative MRI demonstrated a radiographic gross total resection of the tumor. At the six-week postoperative visit, her diplopia had completely resolved. She was referred for adjuvant proton beam radiation therapy.

DiscussionSkull base chondrosarcomas are rare lesions of cartilaginous origin. They are estimated to account for 0.15 percent of intracranial lesions and occur more commonly in males.

Chondrosarcomas are thought to arise from cartilaginous rests that remain after ossification of the skull base. These lesions typically present with cranial neuropathies, particularly diplopia, based on the lesion’s location. They occur most commonly in an off-midline location at the petroclival (medial temporal bone-clivus) junction.

The deep-seated location of skull base chondrosarcomas, along with their close proximity to the carotid artery and cranial nerves, can make these tumors difficult to treat. Varied open skull base and transfacial approaches have been used based on tumor location. More recently, endoscopic endonasal approaches have been used for petrous apex chondrosarcomas.

Endonasal endoscopy takes advantage of an anatomic corridor – the nasal cavity – to access deep-seated lesions of the skull base. Compared to traditional microsurgery, this technology’s improved illumination and magnification often allow for better visualization and resection of skull base lesions.

In this particular case and also common to chondrosarcomas, the lesion was located laterally to the midline. The tumor extended further laterally than the medial internal auditory canal. Such lateral extension is difficult to access with standard endonasal surgery.

We performed a right-sided transmaxillary endoscopic approach to gain access to the left petrous apex. This “cross-court” technique provided excellent access to the long axis of the lesion and allowed our team to maximize the surgical resection.

To our knowledge, this endoscopic transmaxillary approach to the contralateral petrous apex has not been reported previously. The procedure was performed in Providence St. Vincent Medical Center’s 1.5-tesla intraoperative MRI surgical suite to confirm gross total resection at the time of surgery.

Despite the malignant, locally aggressive nature of chondrosarcomas, they are typically slow growing lesions. Reported five-year survival rates typically are greater than 90 percent. However, recurrences as delayed as 10 years after treatment also have been reported. Adjuvant radiation generally is recommended after complete or incomplete surgical resection.

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